Partnership Units and Related Matters - Summary of Distributions Declared and Paid by the Partnership (Details) - Distributions Paid [Member] - USD ($) $ in Millions	3 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019
Distributions Made To Members Or Limited Partners [Abstract]
Distributions payable date	Aug. 13, 2020	May 13, 2020	Feb. 13, 2020
Total Distributions	$ 51.7	$ 53.1	$ 241.9
Distributions to Targa Resources Corp.	$ 48.9	$ 50.3	$ 239.1